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The typical clacks tower is described as "three stories tall, made of wood, and looks like it was put together in a hurry, probably because it was". They are stated usually to be tend to be eight miles apart in flat country.

The ground floor is a storeroom, the second contains an office, a kitchen and, in out-of-the-way towers, a bunkroom. The top floor contains the controls, two chairs face identical control boards on either side, each connected to the panels on the opposite side. There is a keyboard, levers, and pedals. Sometimes entering a code will alter the configuration of the system, probably beneficially (but see Smoking GNU, below.)

The history of the clacks network was detailed in Going Postal. The invention was originally made by an artificer called Robert Dearheart who was conducting experiments in an abandoned wizard's tower halfway between Ankh-Morpork and Sto Lat, where he came up with he basic mechanism of two-by-three array of wooden panels, with pulleys that could drop shutters over them, creating a code. A series of high towers, with one of these mechanisms on each side and someone ready to relay the codes, could send messages across "at the speed of light"; The panel also had a recess for a lamp, meaning messages could be sent at night.

Based on this, he founded the Grand Trunk Company which began creating a network of towers that would stretch across the continent. "High traffic" towers have more than six panels. The largest is the one on the huge hill in Ankh-Morpork called 'The Tump' (a cross between the Tower Trump Tower and the Post Office Tower), which is the main junction between the city's clacks network (various city institutions, including the Guilds, and the Watch had installed small clacks towers on their buildings) and the chain of towers that leads past Sto Lat, into Überwald, and from there to Genua. In the less civilized areas in the heart of the continent, they ran into problems, and most clacks towers in the Überwald area had fortified stone bases and, often, armed guards. In Monstrous Regiment a particularly acute problem in Borogravia is described, where the towers were seen as an 'Abomination unto Nuggan' (the local god), on the grounds that if messages were being sent through the air, prayers would get tangled up in them.

Because much of the material being sent was confidential, the senders would put it in their own code before being given to the clacks operators. The operators were, therefore, often surprised if they received a message they understood, outside the Overhead (the messages from and about the network itself).

The Grand Trunk employed a lot of gargoyles as they were exceptionally good at sitting and watching without getting bored.

The success of the clacks network resulted in a fad for semaphore of all types, and fashionable Morporkians began carrying signal flags with them, to send messages to friends on the other side of the room. This appears to have died out, although the City Watch has its own semaphore network, with a relay station on the roof of the Old Lemonade Factory (the Watch training school).

Dearheart, and his employees, continued to improve the network, and as the network grew larger, activating the shutters directly became too complicated, so methods of automating the process were introduced. Punch cards, nicknamed jacquards, were designed that would send certain messages automatically, and clockwork machinery was added to regulate the mechanisms. Outgoing messages were stored on rolls of punched paper called "drum rolls" (presumably after the differential drum, which seems to be the centre of the clockwork). They even worked out a way of coding pictures by using numbers to represent colours; this was later simplified, as explained in Monstrous Regiment.

Unfortunately, Dearheart and those like him were brilliant at engineering, but not finances. A consortium of financiers had been embezzling from the company since it was set up, and when it reached the point of collapse, they bought Dearheart and the others out with their own money. Under the new management, the clacks network became more profitable, but less reliable. As the new owners didn't really understand the clacks the way the previous management had, they worked it until it broke.

The head of the new consortium was a man named Reacher Gilt. A ruthless businessman with a piratical appearance, including an eyepatch and a parrot (actually a cockatoo that, instead of repeatedly saying "pieces of eight", repeatedly said "twelve and a half percent"), he was a shameless con-artist and fraudster whose business style was described as "Find the lady with entire banks". He maintained his monopoly by killing anyone attempting to set up another network, including Dearheart's son, John, and employing the banshee Mr. Gryle to do so.

Clacks operators, therefore, could either keep working for a company that didn't really care about the clacks, or give up. Since the clacks tended to attract obsessive personalities (a parallel to computer geeks), this was more than some could stand. One group (a trio comprising "Mad Al, Sane Alex, and Undecided Adrian who says he's not mad but can't prove it"), who had been working with John Dearheart before his death, set up an illegal clacks tower and used their knowledge of the system to send unauthorized messages in the Overhead, in a manner akin to computer hackers, crackers, or phreakers. They worked out a way to deliver killer pokes into the system, putting the towers out of commission (the explanation given for one of them is that if two specific shutters are moved in opposite directions at the top of a tower, it would rock dangerously. Repeating this at the right intervals in a long message would cause the tower to collapse). They called themselves the Smoking GNU, from the clacks-jargon term for a really fast unlogged message (the name is a reference to "the smoking gun" in many conspiracy theories; it is likely also a reference to the GNU Project or its related licenses, which are heavily associated with hacker culture, and whose philosophies tend to be counter to monopolistic business practices. The book states that G indicates a message that goes on, N indicates not logged and U indicated that it is turned around at the end of the line.). The Smoking GNU trio are also partly based on The Lone Gunmen, a trio of hackers from The X-Files and later their own TV series.

Alex Carlton and Al Winton are clacks engineers. Despite Alex's nickname, it is Al's opinion that he's mad as well, because nobody normal would organize screws by size (Jeremy Clockson had the same kind of "sanity", and many Discworld villains have similar afflictions). Adrian Emery is an alchemist, and has a number of ideas for improving the clacks with chemicals that change colour (and hardly explode at all).

The clacks system has also been cracked by Hex, after Ponder Stibbons connected it to the Unseen University's tower (thereby making Hex the equivalent of a computer with an internet connection). Whether or not this is actually legal is a question the faculty is carefully not asking.

In Going Postal, the consortium was exposed, and Havelock Vetinari proposed that the Ankh-Morpork Post Office take over the running of the system, most likely a reference to when the GPO (General Post Office) formerly ran the telephone network in the UK. However, the Postmaster, Moist von Lipwig, has expressed his intention to return the Grand Trunk Company to the Dearheart family. Reacher Gilt was presumed dead after being given the opportunity of (having) a lifetime by Lord Vetinari, and declining it.

While the system structure of the clacks is similar to that of the telegraph system, elements of it are often described as similar to the Internet; for example, it threatens to make the Post Office obsolete in Going Postal and is sometimes described as 'c-mail' (a clear reference to e-mail).